Refrigerant cycle system

ABSTRACT

In a refrigerant cycle system, a compression mechanism of an electric compressor sucks and compresses refrigerant, and an electric motor that drives the compression mechanism is cooled by the refrigerant. A variable throttle mechanism decompresses the refrigerant discharged from the electric compressor. A motor temperature detector detects a temperature of the electric motor. A motor protection determiner determines whether the temperature of the electric motor detected by the motor temperature detector is equal to or higher than a criterion value. A motor protection controller controls the variable throttle mechanism so that an opening degree of the variable throttle mechanism does not decrease when the motor protection determiner determines that the temperature of the electric motor is equal to or higher than the criterion value.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by referenceJapanese Patent Application No. 2008-082749 filed on Mar. 27, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a refrigerant cycle system having anelectric compressor.

2. Description of Related Art

Conventionally, in an electric compressor in which a compressionmechanism and an electric motor for driving the compression mechanismare integrated, a temperature protection control is performed asdisclosed in JP2006-291878A and JP2005-248730A, for example. In order toavoid excessive temperature rise of the electric motor, the temperatureprotection control is performed when the temperature of an inverter, theelectric motor, etc., excessively rises due to heavy load condition ofthe electric compressor.

In JP2006-291878A, the temperature of the electric motor is evaluated onthe basis of the motor speed of the electric compressor, the inputcurrent of the inverter, etc. The excessive temperature rise of theelectric motor is avoided by stopping the electric compressor when theevaluated temperature of the electric motor exceeds a predeterminedvalue. In JP2005-248730A, the electric compressor has a construction inwhich refrigerant sucked into the electric compressor cools an inverterthat includes a driving circuit for the electric motor. In the electriccompressor, the motor speed of the electric motor is raised or theelectric compressor is stopped to inhibit the temperature rise of theinverter, which occurs when the rotational speed of the electricconverter is small although the torque that should be generated by theelectric motor is large.

In JP2006-291878A, the electric compressor is stopped in order to avoidthe temperature rise of the electric motor. However, if a refrigerantcycle system having the electric compressor is applied to a vehicularair conditioning system, there is a problem that the air conditioningfeeling etc. in a passenger compartment becomes worse significantly.

The construction of the electric compressor disclosed in JP2005-248730Ais for protecting an inverter device from excessive temperature rise.However, when the temperature of the inverter rises, a current valueinputted into the electric motor is also large. Therefore, heatgeneration in the electric motor is large, and the electric motor is ina high temperature state. In this situation, a temperature protectioncontrol of the electric motor is performed by stopping the electriccompressor as in JP2006-291878A, and the same problem as inJP2006-291878A occurs.

SUMMARY OF THE INVENTION

The present invention is made in view of the above-mentioned problem.Thus, it is an objective of the present invention to provide arefrigerant cycle system that can perform temperature protection controlfor avoiding excessive temperature rise of an electric motor of anelectric compressor without stopping the electric compressor more thannecessary.

To achieve the objective of the present invention, there is provided arefrigerant cycle system that has an electric compressor, a variablethrottle mechanism, a motor temperature detector, a motor protectiondeterminer and a motor protection controller. The electric compressorincludes a compression mechanism, which sucks and compressesrefrigerant, and an electric motor, which drives the compressionmechanism and is cooled by the refrigerant at a suction side of thecompression mechanism. The variable throttle mechanism decompresses therefrigerant discharged from the electric compressor. The motortemperature detector detects a temperature of the electric motor. Themotor protection determiner determines whether the temperature of theelectric motor detected by the motor temperature detector is equal to orhigher than a criterion value. The motor protection controller controlsthe variable throttle mechanism so that an opening degree of thevariable throttle mechanism does not decrease when the motor protectiondeterminer determines that the temperature of the electric motor isequal to or higher than the criterion value.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objectives, features andadvantages thereof, will be best understood from the followingdescription, the appended claims and the accompanying drawings in which:

FIG. 1 is a schematic diagram showing the configuration of a refrigerantcycle system according to a first embodiment of the present invention;

FIG. 2 is a block diagram showing an electric control portion of therefrigerant cycle system according to the first embodiment;

FIG. 3 is a flowchart showing a process for setting an opening degree ofan electric expansion valve of the refrigerant cycle system according tothe first embodiment;

FIG. 4 is a control characteristic diagram showing a motor temperatureassociated with a motor current and a motor speed of an electric motorof an electric compressor of the refrigerant cycle system according tothe first embodiment;

FIG. 5 is a schematic diagram showing the configuration of a refrigerantcycle system according to a second embodiment of the present invention;

FIG. 6 is a flowchart showing a principal part of a process for settingopening degree of an electric expansion valve of the refrigerant cyclesystem according to the second embodiment; and

FIGS. 7A, 7B are control characteristic diagrams showing a motortemperature associated with a motor current and a motor speed of anelectric motor of an electric compressor of the refrigerant cycle systemaccording to the second embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS First Embodiment

A first embodiment of the present invention will be described hereafter,referring to FIGS. 1-4. FIG. 1 is a schematic diagram showing an entireconstruction of a refrigerant cycle system according to the firstembodiment, which is applied to a vehicular air conditioning system. Asshown in FIG. 1, the vehicular air conditioning system according to thefirst embodiment has an interior air conditioning unit 1 that isinstalled inside an instrument panel, which is located at a front-mostpart of a passenger compartment of a vehicle to form an instrument boardetc.

The interior air conditioning unit 1 has a case member 2 that is made ofresin. The case member 2 forms an outer shell of the interior airconditioning unit 1, and houses constituent devices of the interior airconditioning unit 1 therein. This case member 2 defines an air passagethrough which air is blown into the passenger compartment of thevehicle.

An interior/exterior air switching box 3 is installed in the mostupstream portion of the air passage of the case member 2. Theinterior/exterior air switching box 3 has an interior-air inlet port 3 aand an exterior air inlet port 3 b. An interior/exterior air switchingdoor 3 c is rotatably installed in the interior/exterior air switchingbox 3.

The interior/exterior air switching door 3 c is driven by a servomotor(not shown) to switch between an interior air mode, an exterior air modeand an interior/exterior air mode. In the interior air mode, interiorair (air inside the passenger compartment) is introduced through theinterior air inlet port 3 a into the passenger compartment. In theexterior air mode, exterior air (air outside the passenger compartment)is introduced through the exterior air inlet port 3 b into the passengercompartment. In the interior/exterior air mode, both the interior airand the exterior air are introduced into the passenger compartment.

An electric blower 4 is installed at a downstream side of theinterior/exterior air switching box 3. The electric blower 4 blows theair into the passenger compartment. The electric blower (second electricblower) 4 is an electrically-driven blower in which a well-knowncentrifugal multi-blade fan (sirocco fan) is driven by an electric motor4a. The rotational speed of the electric motor 4a can be controlled by acontrol voltage outputted from an air conditioner controller 20, whichwill be described later.

An evaporator 5 is installed at a downstream side of the electric blower4. The evaporator 5 is one of the constituent devices that constitute arefrigerant cycle system 10, which will be described later. Moreover,the evaporator 5 evaporates low-pressure side refrigerant, which hasflowed into the evaporator 5, to absorb heat. Thereby, the evaporator 5functions as a cooling heat exchanger that cools the air blown from theelectric blower 4.

A heater core 6 is installed at a downstream side of the evaporator 5 inan air flow direction. The heater core 6 is a heat exchanger forheating, which heats the air that has passed through the evaporator 5 byusing heat of hot water that is heated by an electric heater etc. Thehot water heated by the electric heater etc. is supplied into the heatercore 6 by an electric pump (not shown).

Bypass passages 7 are arranged on the sides of the heater core 6. Theair flows through the bypass passages 7 to bypass the heater core 6.Moreover, air mixing doors 8 are rotatably arranged on the sides of theheater core 6. The air mixing doors 8 functions as an air temperatureadjusting means. The air mixing door 8 are driven by a servomotor (notshown) so that the rotation position (opening degree) of the air mixingdoor 8 can be continuously adjusted.

By adjusting the opening degree of the air mixing door 8, the ratiobetween the amount of air passing through the heater core 6 and theamount of air passing through the bypass passages 7 is adjusted. Thus,the temperature of the air on a downstream side of the heater core 6 isadjusted. In this embodiment, the bypass passages 7 are arranged on bothsides of the heater core 6. Accordingly, also the air mixing doors 8 arearranged on both sides of the heater core 6, and the two air mixingdoors 8 are controlled in conjunction with each other.

A defroster blowing-out port (not shown), a face blowing-out port (notshown) and a foot blowing-out port (not shown) are arranged at the mostdownstream part of the air passage of the case member 2. Conditioned airis blown out toward a front window glass (windshield) of the vehiclethrough the defroster blowing-out port, toward an upper body of thepassenger through the face blowing-out port, and toward feet of thepassenger through the foot blowing-out port. Opening/closing doors arerotatably arranged at upstream sides of these blowing-out ports. Theopening/closing doors open or close by being driven by a commonservomotor through the medium of a link mechanism (not shown).

Next, the refrigerant cycle system 10 will be described. The refrigerantcycle system 10 has an electric compressor 11, an exterior-side heatexchanger 13, an electric expansion valve 16, an accumulator 18, etc.,in addition to the above-mentioned evaporator 5.

In the electric compressor 11, an electric motor 11 a and a compressionmechanism 11 b, which is driven by the electric motor 11 a, areintegrated. The electric motor 11 a is located at a suction side of theelectric compressor 11, and is cooled by cold refrigerant that is drawninto the electric compressor 11.

The electric motor 11 a is a three phase AC motor. The compressionmechanism 11 b is a well-known scroll compression mechanism, forexample. Moreover, the rotational speed of the electric motor 11 a isvariably controlled by an inverter unit 19, which will be describedlater.

The exterior-side heat exchanger 13 is connected with a discharge sideof the electric compressor 11. At the exterior-side heat exchanger 13,the refrigerant, which is discharged from the electric compressor 11 andhas high temperature and high pressure, exchanges heat with the exteriorair (air outside the passenger compartment). Thus, the exterior-sideheat exchanger 13 functions as a heat-radiating heat exchanger. Theexterior air is blown to the exterior-side heat exchanger 13 by anelectrically-driven cooling fan (first electric blower) 13 a. Thecooling fan 13a is driven by an electric motor 13 b. The rotationalspeed of the electric motor 13 b is controlled by the controlled voltagethat is outputted from the air conditioner controller 20, which will bedescribed later.

The electric expansion valve 16, which functions as a variable throttlemechanism, is connected with an outlet side of the exterior-side heatexchanger 13. The electric expansion valve 16 functions as a pressurecontrol valve. An opening degree of the pressure control valve iselectrically controlled so that discharge refrigerant pressure Pd, whichis the pressure of refrigerant at the discharge side of the electriccompressor 11, would be a target high pressure in a normal operationtime of the refrigeration cycle. The electric expansion valve 16 alsofunctions as a control valve, which inhibits temperature rise of theelectric motor 11 a of the electric compressor 11 when the temperatureof the electric motor 11 a is high.

Specifically, the electric expansion valve 16 includes an electricactuator mechanism 16 a and a valve mechanism that is driven by theelectric actuator mechanism 16 a. A stepping motor serves as theelectric actuator mechanism 16 a, for example. An opening degree of thevalve mechanism can be minutely adjusted in accordance with a workingangle of the electric actuator mechanism 16 a. The opening degree of theelectric expansion valve 16 is controlled by the air conditionercontroller 20, which will be described later.

The above-mentioned evaporator 5 is connected with an outlet side of theelectric type expansion valve 16. The accumulator 18 is connected withthe outlet side of the evaporator 5. The accumulator 18 is a gas/liquidseparation means, which separates the refrigerant discharged from theevaporator 5 into gas refrigerant (saturated gas-phase refrigerant) andliquid refrigerant (saturated liquid-phase refrigerant), and accumulatesexcessive refrigerant in the refrigeration cycle. The gas refrigerantseparated in the accumulator 18 is introduced to the suction side of theelectric compressor 11.

An outline of an electrical control unit according to the firstembodiment will be described hereafter. FIG. 2 is a block diagramshowing the electric control portion. The air conditioner controller 20is composed of a well-known microcomputer that includes a CPU, a ROM, aRAM, etc. and a periphery circuit of the microcomputer. The airconditioner controller 20 performs various calculations and processesbased on a control program that is memorized in the ROM, to controloperations of electric devices such as the inverter unit 19 of theelectric compressor 11, the electric motor 13 b of the cooling fan 13 a,the electric actuator mechanism 16 a of the electric expansion valve 16and the electric motor 4 a of the electric blower 4.

The inverter unit 19 of the electric compressor 11 will be brieflydescribed hereafter. The electric motor 11 a of the electric compressor11, which is a three phase AC motor, is rotationally driven by threephase AC electric power that is converted by and outputted from a powerdevice 190 of the inverter unit 19. The rotational speed of the electricmotor 11 a is minutely and variably controlled by an inverter controlportion 191 (adjustable-speed drive controlling).

The inverter control portion 191 includes a CPU 192, a communicationcircuit 193, etc. The inverter control portion 191 communicates with theair conditioner controller 20 and controls the rotational speed of theelectric motor 11 a of the electric compressor 11 so that the rotationalspeed would be adjusted to an optimum value.

The inverter control portion 191 detects motor current, which isoutputted to the electric motor 11 a, and the rotational speed of theelectric motor 11 a, and outputs the detection values to the airconditioner controller 20. The power source of the inverter unit 19 is abattery 21 that is mounted on the vehicle.

An input side of the air conditioner controller 20 is connected with adischarge pressure sensor 31, an exterior-side refrigerant temperaturesensor 32, a post-evaporator air temperature sensor 33, etc. Thedischarge pressure sensor 31 is for detecting the discharge refrigerantpressure Pd. The exterior-side refrigerant temperature sensor 32 is fordetecting exterior-side refrigerant temperature Tho, which is thetemperature of the refrigerant at the outlet side of the exterior-sideheat exchanger 13. The post-evaporator air temperature sensor 33 is fordetecting blown-out air temperature Te, which is the temperature of theair blown from the evaporator 5.

The detection signals of sensors 34, which include an exterior airtemperature sensor, an interior air temperature sensor, a solarradiation sensor, etc., are also inputted to the air conditionercontroller 20. These sensors 31-34 serve as various detection means inthe first embodiment. Furthermore, an air conditioner operating panel 40is arranged near the instrument board (instrument panel) in thepassenger compartment. Various air conditioner operation signals areinputted from operation members of the air conditioner operating panel40 to the air conditioner controller 20.

Specifically, the various air conditioner operation signals inputted bythe air conditioner operating panel 40 include an interior temperaturesetting signal, an airflow volume switching signal of the electricblower 4, an air blow mode switching signal, an interior/exterior airintroducing mode switching signal of the interior/exterior air switchingbox 3, etc. The interior temperature setting signal is set by atemperature setting switch. The airflow volume switching signal is setby an airflow selector switch. The air blow mode switching signal is setby an air blow mode selector switch. The interior/exterior airintroducing mode switching signal is set by an interior/exterior airselector switch.

Next, the operation of the refrigerant cycle system according to thefirst embodiment, which has the above-described construction, will bedescribed hereafter. First, a basic operation of the refrigerant cyclesystem 10 will be described hereafter. When the operation member (airconditioner switch) of the air conditioner operating panel 40 isswitched and the compressor activation commanding signal is generated,the electric motor 11 a is electrically energized through the inverterunit 19, and the electric motor 11 a rotates. The driving force of theelectric motor 11 a is transmitted to the compression mechanism 11 b,and the electric compressor 11 is driven.

The refrigerant is compressed by the electric compressor 11, and therefrigerant has high temperature and high pressure. The refrigeranthaving the high temperature and the high pressure flows into theexterior-side heat exchanger 13. At the exterior-side heat exchanger 13,the refrigerant exchanges heat with the exterior air that is blown bythe cooling fan 13 a, so as to radiate heat to the exterior air.

Then, the refrigerant discharged from the exterior-side heat exchanger13 is decompressed by the electric expansion valve 16 and brought into agas-liquid two-phase state having low temperature and low pressure. Thegas-liquid two-phase refrigerant having the low temperature and the lowpressure flows into the evaporator 5. At the evaporator 5, therefrigerant is vaporized by absorbing heat of the air that is blown fromthe electric blower 4. Thereby, the air blown from the electric blower 4is cooled down by the evaporator 5, and the cooled air can be blown intothe passenger compartment.

Then, the low-pressure refrigerant that has passed through theevaporator 5 flows into the accumulator 18. At the accumulator 18, thelow-pressure refrigerant is separated into the saturated liquid-phaserefrigerant and the saturated gas-phase refrigerant. The saturatedgas-phase refrigerant is introduced from an outlet of the accumulator 18to the suction side of the electric compressor 11. Then, the saturatedgas-phase refrigerant is sucked into the electric compressor 11 and iscompressed again.

Next, basic control process performed by the air conditioner controller20 according to the first embodiment will be described hereafter. Thiscontrol process begins when the air conditioner switch is turned onunder the condition that a starter switch (not shown) of the vehicle isturned on.

First, a flag, a timer, etc. are initialized. Then, detection signals ofthe sensors 31-34 and operation signals of the air conditioner operatingpanel 40 are read in. Then, control states of the actuators 4 a, 13 b,16 a, 19 etc. are determined.

Specifically, a target blowing-out temperature TAO, at which the airshould be blown into the passenger compartment, is calculated based ontarget air temperature Tset in the passenger compartment, interior airtemperature Tr and exterior air temperature Tam. Furthermore, based onthe target blowing-out temperature TAO, a target rotational speed of theelectric blower 4 (voltage applied to the electric motor 4 a), a targetrotational speed of the cooling fan 13 a of the exterior-side heatexchanger 13 (voltage applied to the cooling fan 13 a), a target openingdegrees of the air mixing doors 8 (control signals outputted to theservomotor for the air mixing doors 8) are determined.

Furthermore, based on the target blowing-out temperature TAO, a targetevaporator blowing-out temperature TEO is determined. The targetblowing-out temperature TEO is a target value of cooling degree of theevaporator 5. Then, a refrigerant discharge capacity of the electriccompressor 11 (control signal that is outputted to the inverter unit 19)is calculated so that the blowing-out air temperature Te of theevaporator 5 would approach the target evaporator blowing-outtemperature TEO.

Moreover, based on the exterior-side refrigerant temperature Tho(temperature of the refrigerant at the outlet side of the exterior-sideheat exchanger 13), a target high pressure Po is determined. By thetarget high pressure Po, efficiency of the refrigeration cycle (COP) ismaximized. The opening degree of the electric expansion valve 16(control signal that is outputted to the electric actuator mechanism 16a) is determined so that the discharge refrigerant pressure Pd of theelectric compressor 11 would become the above-mentioned target highpressure Po.

Then, output signals are outputted from the air conditioner controller20 to the actuators 4 a, 11 a, 13 b, 16 a, etc. so as to realize thecontrol states of the actuators 4 a, 13 b, 16 a, 19 etc., which havebeen already determined.

In the electric compressor 11 in the first embodiment, the electricmotor 11 a is cooled by the cold refrigerant that is drawn into theelectric compressor 11. When the motor current, which is outputted fromthe inverter unit 19 to the electric motor 11 a, is large and therotational speed of the electric motor 11 a is small, occasionally theelectric motor 11 a is not sufficiently cooled down by the coldrefrigerant that is drawn into the electric compressor 11, and theelectric motor 11 a can be in a high temperature state.

In such a case, the electric compressor 11 is stopped in a conventionalrefrigerant cycle system. In the first embodiment, the opening degree ofthe electric expansion valve 16 is controlled instead, to perform atemperature protection control for avoiding temperature rise of theelectric motor 11 a of the electric compressor 11.

The temperature protection control for the electric motor 11 a in thefirst embodiment will be described hereafter with reference to FIGS. 3,4. FIG. 3 is a flowchart showing a process for setting the openingdegree of the electric expansion valve 16, which is performed by the airconditioner controller 20. FIG. 4 is a control characteristic diagramshowing the temperature of the electric motor 11 a associated with themotor current and the rotational speed of the electric motor 11 a of theelectric compressor 11 in the first embodiment.

The process for setting the opening degree of the electric expansionvalve 16, which is shown in FIG. 3, begins when the refrigeration cycleis started, that is, when the electric compressor 11 is started. First,at step S100, the air conditioner controller 20 reads the detectionsignals of the sensors, the various air conditioner operation signalssent from the air conditioner operating panel 40, etc.

Specifically, the air conditioner controller 20 reads the dischargerefrigerant pressure Pd that is detected by the discharge pressuresensor 31, the exterior-side refrigerant temperature Tho (temperature ofthe refrigerant at the outlet side of the exterior-side heat exchanger13) that is detected by the exterior-side refrigerant temperature sensor32, the value of the motor current that is outputted from the inverterunit 19 to the electric motor 11 a, the rotational speed of the electricmotor 11 a, etc.

Next, at step S200, the air conditioner controller 20 calculates acontrol amount of the opening degree of the electric expansion valve 16so that the discharge refrigerant pressure Pd, which is detected by thedischarge pressure sensor 31, would become the target high pressure Po,which is determined based on the exterior-side refrigerant temperatureTho (temperature of the refrigerant at the outlet side of theexterior-side heat exchanger 13) that is detected by the exterior-siderefrigerant temperature sensor 32. In the first embodiment, the openingdegree of the electric expansion valve 16 is increased when the controlamount of the opening degree is larger than zero, and the opening degreeof the electric expansion valve 16 is decreased when the control amountof the opening degree is smaller than zero.

Moreover, in the first embodiment, the control characteristic shown inFIG. 4 is memorized beforehand in the ROM etc. of the air conditionercontroller 20. In this control characteristic, the temperature of theelectric motor 11 a is associated with the rotational speed and themotor current of the electric motor 11 a, which are detected by theinverter unit 19. The temperature of the electric motor 11 a isinversely proportional to a flow rate of the refrigerant, namely, therotational speed of the electric motor 11 a. The temperature of theelectric motor 11 a is proportional to a heat generation in the electricmotor 11 a, namely, a square of the value of the motor current. Forexample, the temperature of the electric motor 11 a becomes low when therotational speed of the electric motor 11 a is large and the motorcurrent is small. The temperature of the electric motor 11 a becomeshigh when the rotational speed of the electric motor 11 a is small andthe motor current is large.

In the first embodiment, the temperature of the electric motor 11 a iscalculated and detected based on the control characteristic.Alternatively, the temperature of the electric motor 11 a may becalculated by inputting the rotational speed of the electric motor 11 aand the value of the motor current into a computing equation, etc.

In the control characteristic, criterion values of the temperature ofthe electric motor 11 a are specified in order to determine whether thetemperature rise of the electric motor 11 a should be avoided or not.Specifically, in the control characteristic of the first embodiment,first to third criterion values are specified as the criterion values ofthe temperature of the electric motor 11 a, and a limit value of thetemperature of the electric motor 11 a is also specified.

The relation between the criterion values and the limit value is: (firstcriterion value)<(second criterion value)<(third criterion value)<(limitvalue). The first to third criterion values and the limit value of thetemperature of the electric motor 11 a are specified so that therotational speed of the electric motor 11 a would increases as the valueof the motor current increases on a condition that the temperature ofthe electric motor 11 a is kept at either one of the first to thirdcriterion values and the limit value. A first criterion line, whichindicates the rotational speed and the motor current of the electricmotor 11 a that correspond to the first criterion value, a secondcriterion line, which indicates the rotational speed and the motorcurrent of the electric motor 11 a that correspond to the secondcriterion value, a third criterion line, which indicates the rotationalspeed and the motor current of the electric motor 11 a that correspondto the third criterion value, and a limit line, which indicates therotational speed and the motor current of the electric motor 11 a thatcorrespond to the limit value, are in parallel with each other.

The first to third criterion lines and the limit line separate thetemperature of the electric motor 11 a of the electric compressor 11into ranges A-D and an off-limit range. Specifically, in the range A,the temperature of the electric motor 11 a is lower than the firstcriterion value on the basis of the control characteristic thatassociates the temperature of the electric motor 11 a with therotational speed and the motor current of the electric motor 11 a. Inthe range B, the temperature of the electric motor 11 a is equal to orhigher than the first criterion value and is lower than the secondcriterion value. In the range C, the temperature of the electric motor11 a is equal to or higher than the second criterion value and is lowerthan the third criterion value. In the range D, the temperature of theelectric motor 11 a is equal to or higher than the third criterion valueand is lower than the limit value. In the off-limit range, which is adiagonally shaded area in FIG. 4, the temperature of the electric motor11 a is equal to or higher than the limit value.

The ranges A-D and the off-limit range are indices that indicate thestates of the temperature of the electric motor 11 a of the electriccompressor 11. The range A indicates a normal state of the temperatureof the electric motor 11 a. The off-limit range indicates an abnormalstate of the temperature of the electric motor 11 a, in which thetemperature of the electric motor 11 a is excessively high (at 120° C.,for example) and an insulation failure of a winding can occur in theelectric motor 11 a. The ranges B-D are set between the range A and theoff-limit range, and indicate a state where the temperature protectioncontrol for the electric motor 11 a is necessary.

At step S300 in FIG. 3, the air conditioner controller 20 calculates anddetects current temperature of the electric motor 11 a in accordancewith the rotational speed and the motor current of the electric motor 11a on the basis of the control characteristic. Then, the air conditionercontroller 20 calculates the current temperature of the electric motor11 a is in which range of the above-mentioned control characteristic.Then, at step S400, the air conditioner controller 20 determines whetherthe temperature of the electric motor 11 a, which has been calculated atstep S300, is in the range A or not.

If it is determined at step S400 that the temperature of the electricmotor 11 a is in the range A, the air conditioner controller 20 sets thecontrol amount that has been calculated at step S200 as the controlamount of the opening degree of the electric expansion valve 16 (stepS500). That is, the discharge refrigerant pressure Pd of the electriccompressor 11 can be maintained at the target high pressure Po, whichrealizes the optimal control of the refrigeration cycle.

If it is not determined at step S400 that the temperature of theelectric motor 11 a is in the range A, the air conditioner controller 20determines at step S410 whether the control amount of the opening degreeof the electric expansion valve 16, which has been calculated at stepS200, is larger than zero or not. If it is determined at step S410 thatthe control amount is smaller than zero, the opening degree of theelectric expansion valve 16 is being controlled to decrease. Thus, atstep S420, the air conditioner controller 20 sets the control amount atzero so as to change the control amount to a value that will not changethe opening degree of the electric expansion valve 16. If it isdetermined at step S410 that the control amount is larger than or equalto zero, the air conditioner controller 20 does not change the controlamount, and the process goes to step S430.

Next, at step S430, the air conditioner controller 20 determines whetherthe temperature of the electric motor 11 a is in the range B or not. Ifit is determined at step S430 that the temperature of the electric motor11 a is in the range B, the process goes to step S500, and the airconditioner controller 20 sets the control amount that is larger than orequal to zero as the control amount of the opening degree of theelectric expansion valve 16.

Thus, if the temperature of the electric motor 11 a is in the range B,at least the opening degree of the electric expansion valve 16 iscontrolled not to decrease. That is, at least the increase of thedischarge refrigerant pressure Pd of the electric compressor 11 isinhibited, so that it is possible to avoid the load increase of theelectric compressor 11 and the temperature rise of the electric motor 11a.

If it is not determined at step S430 that the temperature of theelectric motor 11 a is in the range B, the air conditioner controller 20determines at step S440 whether the temperature of the electric motor 11a is in the range C or not. If it is determined at step S440 that thetemperature of the electric motor 11 a is in the range C, at step S450,the air conditioner controller 20 adds a first predetermined value alphato the control amount of the opening degree of the electric expansionvalve 16, which has been calculated at step S200, or adds the firstpredetermined value alpha to the control amount that has been set atzero at step S420.

Then, the process goes to step S500, and the air conditioner controller20 sets the control amount, to which the first predetermined value alphais added, as the control amount of the opening degree of the electricexpansion valve 16. Thus, if the temperature of the electric motor 11 ais in the range C, the opening degree of the electric expansion valve 16is controlled to increase. That is, the discharge refrigerant pressurePd of the electric compressor 11 is decreased, so that it is possible todecrease the load of the electric compressor 11 and to avoid thetemperature rise of the electric motor 11 a.

If it is not determined at step S440 that the temperature of theelectric motor 11 a is in the range C, the air conditioner controller 20determines at step S460 whether the temperature of the electric motor 11a is in the range D or not. If it is determined at step S460 that thetemperature of the electric motor 11 a is in the range D, at step S470,the air conditioner controller 20 adds a second predetermined value betato the control amount of the opening degree of the electric expansionvalve 16, which has been calculated at step S200, or adds the secondpredetermined value beta to the control amount that has been set at zeroat step S420.

Then, the process goes to step S500, and the air conditioner controller20 sets the control amount, to which the second predetermined value betais added, as the control amount of the opening degree of the electricexpansion valve 16. The second predetermined value beta, which is addedat step S460, is a value larger than the first predetermined valuealpha, which is added at step S450 ((first predetermined valuealpha)<(second predetermined value beta)). Thus, if the temperature ofthe electric motor 11 a is in the range D, the opening degree of theelectric expansion valve 16 is controlled to increase more than when thetemperature of the electric motor 11 a is in the range C.

That is, by gradually decreasing the discharge refrigerant pressure Pdof the electric compressor 11, it become possible to avoid thetemperature rise of the electric motor 11 a by decreasing the load ofthe electric compressor 11, and to prevent a sudden change of thedischarge refrigerant pressure Pd of the electric compressor 11, whichdegrades the air conditioning feeling etc. in the passenger compartment.

If it is not determined at step S460 that the temperature of theelectric motor 11 a is in the range D, the air conditioner controller 20determines at step S480 that the temperature of the electric motor 11 ais abnormal, and memorizes the abnormality in the ROM etc. of the airconditioner controller 20.

If the temperature of the electric motor 11 a is in the off-limit range,it is anticipated that the refrigerant cycle system 10 can break down.Therefore, the operation of the electric compressor 11 is stopped. Thedetermination processes at steps S400, S430, S440, S460 correspond to aprotection determining means, and the processes at steps S420, S450,S470 correspond to a motor protection control means.

As described above, when the temperature of the electric motor 11 a ofthe electric compressor 11 is equal to or higher than the firstcriterion value, at least the opening degree of the electric expansionvalve 16 is controlled not to decrease. Thus, it is possible to avoidthe increase of the discharge refrigerant pressure Pd of the electriccompressor 11. Thereby, at least the increase of the load of theelectric compressor 11 is avoided, and it is possible to avoid theincrease of the motor current that is outputted to the electric motor 11a. Therefore, it is possible to perform the temperature protectioncontrol for avoiding temperature rise of the electric motor 11 a withoutstopping the electric compressor 11.

Moreover, the temperature of the electric motor 11 a is calculated anddetected on the basis of the control characteristic that associates thetemperature of the electric motor 11 a with the rotational speed and themotor current of the electric motor 11 a. Thus, it is possible toperform the temperature protection control for avoiding temperature riseof the electric motor 11 a when the temperature of the electric motor 11a is equal to or higher than a criterion value.

Moreover, in detecting the temperature of the electric motor 11 a on thebasis of the control characteristic, it is possible to perform thetemperature protection control for avoiding temperature rise of theelectric motor 11 a without providing the electric motor 11 a with adetecting device exclusively for detecting the temperature of theelectric motor 11 a. Thus, it is possible to simplify the constructionof the electric compressor 11.

Moreover, by specifying more than two criterion values (the first tothird criterion values) as the criterion value in the controlcharacteristic, it is possible to gradually adjust the opening degree ofthe electric expansion valve 16. Therefore, it is possible to inhibitthe air conditioning feeling etc. in the passenger compartment frombecoming degraded. In the first embodiment, the first to third criterionvalues are specified as the criterion value. The present invention isnot limited to this, and it is also possible to increase or decrease thenumber of the criterion value(s).

Second Embodiment

Next, a second embodiment of the present invention will be describedhereafter, referring to FIGS. 5-7. Elements that are substantially thesame as or equivalent to those in the first embodiment have the samereference numerals as in the first embodiment, and are not describedagain. FIG. 5 is a schematic diagram showing an entire construction of arefrigerant cycle system according to the second embodiment, which isapplied to a vehicular air conditioning system. The refrigerant cyclesystem 10 according to the second embodiment is configured as a heatpump refrigeration cycle that can be switched between a coolingoperation mode and a heating operation mode.

As shown in FIG. 5, in the second embodiment, a heater core 6 isarranged in a case member 2 of an interior air conditioning unit 1. Theheater core 6 is one of the constituent devices that constitute therefrigerant cycle system 10. The heater core 6 functions as a use-sideheat exchanger, which heats the air that has passed through anevaporator 5 by using the refrigerant having high temperature and highpressure as a heat source. The heater core 6 functions also as aheat-radiating heat exchanger, which cools the refrigerant by radiatingheat to the air that has passed through the evaporator 5.

The refrigerant cycle system 10 according to the second embodiment hasthe evaporator 5, the heater core 6, an electric compressor 11, a firstelectric expansion valve 12, an exterior-side heat exchanger 13, aninterior heat exchanger 15, a second electric expansion valve 16, whichcorresponds to the electric expansion valve in the first embodiment, anaccumulator 18, etc. In the following description, the heater core 6 isexplained as a use-side heat exchanger.

An inlet side of the above-mentioned use-side heat exchanger 6 isconnected with a discharge side of the electric compressor 11. The firstelectric expansion valve 12, which functions as a variable throttlemechanism, is connected with an outlet side of the use-side heatexchanger 6.

The first electric expansion valve 12 functions also as a high pressurecontrol valve. The opening degree of the high pressure control valve iselectrically controlled by control signals that are outputted from anair conditioner controller 20 so that discharge refrigerant pressure Pdof the refrigeration cycle would become a target high pressure Po in theheating operation mode, which will be described later. The firstelectric expansion valve 12 includes an electric actuator mechanism 12 aand a valve mechanism.

The exterior-side heat exchanger 13 is connected with an outlet side ofthe first electric expansion valve 12. The refrigerant cycle system 10according to the second embodiment has a first bypass passage 14 a. Thefirst bypass passage 14 a connects the outlet side of the use-side heatexchanger 6 directly with an inlet side of the exterior-side heatexchanger 13 so that the refrigerant can bypass the first electricexpansion valve 12. A first open/close valve 14 is arranged in the firstbypass passage 14 a to open and close the first bypass passage 14 a. Thefirst open/close valve 14 is an electromagnetic valve that is controlledto be opened and closed by control voltage that is outputted from theair conditioner controller 20.

In the cooling operation mode, which will be described later, theexterior-side heat exchanger 13 functions as a heat-radiating heatexchanger that cools the refrigerant by radiating heat of therefrigerant to the exterior air in an analogous fashion as in the firstembodiment. In the heating operation mode, the exterior-side heatexchanger 13 functions as a heat-absorbing heat exchanger that vaporizesthe refrigerant by absorbing heat from the exterior air.

A first refrigerant passage 15 a of the interior heat exchanger 15 isconnected with an outlet side of the exterior-side heat exchanger 13. Inthe cooling operation mode, which will be described later, the interiorheat exchanger 15 cools the refrigerant at the outlet side of theexterior-side heat exchanger 13 by exchanging heat between therefrigerant at the outlet side of the exterior-side heat exchanger 13,which passes through the first refrigerant passage 15 a of the interiorheat exchanger 15, and the refrigerant at a suction side of the electriccompressor 11, which passes through a second refrigerant passage 15 b ofthe interior heat exchanger 15.

The second electric expansion valve 16, which functions as a variablethrottle mechanism, is arranged at an outlet side of the firstrefrigerant passage 15 a of the interior heat exchanger 15. The secondelectric expansion valve 16 has substantially the same construction asthe first electric expansion valve 12, and has an electric actuatormechanism 16 a and a valve mechanism.

In the cooling operation mode, which will be described later, the secondelectric expansion valve 16 functions also as a high pressure controlvalve. The opening degree of the high pressure control valve iselectrically controlled by the control signals that are outputted fromthe air conditioner controller 20 so that the discharge refrigerantpressure Pd would become the target high pressure Po. The evaporator 5is connected with an outlet side of the second electric expansion valve16.

Furthermore, the refrigerant cycle system 10 according to the secondembodiment has a second bypass passage 17 a. The second bypass passage17 a connects an inlet side of the first refrigerant passage 15 a of theinterior heat exchanger 15 directly with an outlet side of theevaporator 5 so that the refrigerant can bypass the second electricexpansion valve 16. Moreover, a second open/closing valve 17 is arrangedin the second bypass passage 17 a to open and close the second bypasspassage 17 a.

The second open/close valve 17 has substantially the same constructionas the first open/close valve 14, and is an electromagnetic valve thatis controlled to be opened and closed by control voltage that isoutputted from the air conditioner controller 20. The accumulator 18 isarranged at a downstream side of the evaporator 5 and the second bypasspassage 17 a. Moreover, an inlet side of the second refrigerant passage15 b of the interior heat exchanger 15 is connected with an outlet ofthe accumulator 18, from which gas-phase refrigerant flows out. Thesuction side of the electric compressor 11 is connected with an outletside of the second refrigerant passage 15 b.

The air conditioner controller 20 performs various calculations andprocesses based on a control program that is memorized in the ROM, tocontrol operations of the above-mentioned actuators 4 a, 11 b, 12 a, 13a, 14, 16 a, 17, etc.

Moreover, an input side of the air conditioner controller 20 isconnected with a suction pressure sensor 35, a suction refrigeranttemperature sensor 36, a discharge refrigerant temperature sensor 37, ause-side refrigerant temperature sensor 38, etc., in addition to theconstruction of the first embodiment. The suction pressure sensor 35 isfor detecting suction refrigerant pressure Ps of the electric compressor11. The suction refrigerant temperature sensor 36 is for detectingsuction refrigerant temperature sensor Ts of the electric compressor 11.The discharge refrigerant temperature sensor 37 is for detectingdischarge refrigerant temperature Td of the electric compressor 11. Theuse-side refrigerant temperature sensor 38 is for detecting fordetecting use-side refrigerant temperature Tco. Detection signals ofthese sensors 35-38, etc. are inputted to the input side of the airconditioner controller 20.

Furthermore, an air conditioner operating panel 40 is provided with acooling/heating selecting switch, etc. The cooling/heating selectingswitch is for selectively switching between the heating operation mode,in which the air to be blown into the passenger compartment is heated,and the cooling operation mode, in which the air to be blown into thepassenger compartment is cooled.

Next, the operation of the refrigerant cycle system 10 according to thesecond embodiment, which has the above-described construction, will bedescribed hereafter. First, a basic operation of the refrigerant cyclesystem 10 when the cooling/heating selecting switch of the airconditioner operating panel 40 is switched to the cooling operation modewill be described hereafter.

In the cooling operation mode, the first open/close valve 14 is opened,the first electric expansion valve 12 is fully closed, and the secondopen/close valve 17 is closed. Thus, in the cooling operation mode, therefrigerant, which has been compressed in the electric compressor 11 andhas high temperature and high pressure, radiates heat to the air in theuse-side heat exchanger (heater core) 6. The refrigerant that has flowedout from the use-side heat exchanger 6 flows into the exterior side heatexchanger 13 through the first bypass passage 14 a, and further radiatesheat to the exterior air and is cooled.

The refrigerant that has flowed out from the exterior-side heatexchanger 13 flows into the first refrigerant passage 15 a of theinterior heat exchanger 15, and exchanges heat with the suctionrefrigerant of the electric compressor 11, which is going to be suckedinto the electric compressor 11 and is passing through the secondrefrigerant passage 15 b, and is further cooled, so that the enthalpy ofthe refrigerant is decreased. Thus, the enthalpy difference(refrigeration capacity) between the refrigerant at the inlet of theevaporator 5 and the refrigerant at the outlet of the evaporator 5 isincreased.

The refrigerant that has flowed out from the first refrigerant passage15 a of the interior heat exchanger 15 is depressurized at the secondelectric expansion valve 16. The refrigerant that has been depressurizedat the second electric expansion valve 16 flows into the evaporator 5,and absorbs heat from the air and evaporates. Therefore, the air that isblown into the passenger compartment is cooled. Thus, the refrigerantthat has flowed out from the evaporator 5 flows into the accumulator 18,and gas-phase refrigerant is separated from liquid-phase refrigerant.Furthermore, the gas-phase refrigerant that has flowed out from theaccumulator 18 is sucked into the electric compressor 11 through thesecond refrigerant passage 15 b of the interior heat exchanger 15.

In the heating operation mode, the first open/close valve 14 is closed,the second open/close valve 17 is opened and the second electricexpansion valve 16 is fully closed. Thus, in the heating operation mode,the refrigerant, which has been compressed in the electric compressor 11and has high temperature and the high pressure, radiates heat to the airin the use-side heat exchanger 6.

The refrigerant that has flowed out from the use-side heat exchanger 6is depressurized at the first electric expansion valve 12. Therefrigerant that has been depressurized at the first electric expansionvalve 12 absorbs heat at the exterior-side heat exchanger 13 from theexterior air, and is vaporized. The refrigerant that has flowed out fromthe exterior-side heat exchanger 13 flows through the second bypasspassage 17 a, the accumulator 18 and the second refrigerant passage 15 bof the interior heat exchanger 15 in sequence, and is sucked into theelectric compressor 11.

Next, the temperature protection control in the second embodiment, inwhich the first and second electric expansion valves 12, 16 operates toprotect the electric motor 11 a of the electric compressor 11, will bedescribed hereafter with reference to FIGS. 6, 7A, 7B. FIG. 6 is aflowchart showing a process for setting the opening degrees of the firstand second electric expansion valves 12, 16, which is performed by theair conditioner controller 20 in the second embodiment. FIGS. 7A, 7B arecontrol characteristic diagrams showing criterion values of the motorcurrent of the electric motor 11 a of the electric compressor 11 in thesecond embodiment, which are set in association with the rotationalspeed of the electric motor 11 a. FIG. 7A shows the controlcharacteristic diagram in the cooling operation mode. FIG. 7B shows thecontrol characteristic diagram in the heating operation mode.

First, at step S100, the air conditioner controller 20 reads thedetection signals of the sensors, the various air conditioner operationsignals sent from the air conditioner operating panel 40, etc.

Specifically, the air conditioner controller 20 reads dischargerefrigerant pressure Pd that is detected by a discharge pressure sensor31, exterior-side refrigerant temperature Tho that is detected by anexterior-side refrigerant temperature sensor 32, use-side refrigeranttemperature Tco that is detected by a use-side refrigerant temperaturesensor 38, the value of the motor current that is outputted from theinverter unit 19 to the electric motor 11 a, the rotational speed of theelectric motor 11 a, etc. Moreover, the air conditioner controller 20detects whether the cooling/heating selecting switch of the airconditioner operating panel 40 is switched to the cooling operation modeor to the-heating operation mode.

Next, at step S110, the air conditioner controller 20 determines whetherthe cooling/heating selecting switch of the air conditioner operatingpanel 40 is switched to the cooling operation mode or not. If it isdetermined that the cooling/heating selecting switch of the airconditioner operating panel 40 is switched to the cooling operationmode, the air conditioner controller 20 calculates at step S210 acontrol amount of the opening degree of the second electric expansionvalve 16 so that the discharge refrigerant pressure Pd of the electriccompressor 11 can become the target high pressure Po, which isdetermined based on the exterior-side refrigerant temperature Tho of theexterior-side heat exchanger 13.

In the second embodiment, the refrigerant that has flowed out from theexterior-side heat exchanger 13 exchanges heat at the interior heatexchanger 15 with the suction refrigerant of the electric compressor 11in the cooling operation mode. Therefore, the suction refrigerant of theelectric compressor 11 is heated by the refrigerant that has flown outfrom the exterior-side heat exchanger 13, and the temperature of thesuction refrigerant is higher than that in the heating operation mode.Accordingly, in the cooling operation mode, the discharge refrigeranttemperature is higher than that in the heating operation mode, so thatthe temperature of the electric motor 11 a rises more than in theheating operation mode. That is, the temperature of the suctionrefrigerant of the electric compressor 11 in the cooling operation modeis different from that in the heating operation mode, and thetemperature of the electric motor 11 a in the cooling operation mode isdifferent from that in the heating operation mode even if each the motorcurrent and the rotational speed of the electric motor 11 a is the same.

For this reason, in the second embodiment, the control characteristicfor the cooling operation mode (see FIG. 7A) and the controlcharacteristic for the heating operation mode (see FIG. 7B) areseparately memorized beforehand in the ROM etc. of the air conditionercontroller 20. As shown in FIGS. 7A, 7B, the criterion temperature inthe control characteristic for the cooling operation mode is lower thanthe criterion temperature in the control characteristic for the heatingoperation mode. Two or more control characteristics in which thecriterion values are different are memorized in ROM etc. of the airconditioner controller 20 for each operation mode.

Next, at step S310, the air conditioner controller 20 selects thecontrol characteristic for the cooling operation mode. Then, based onthe selected control characteristic, the air conditioner controller 20calculates and detects the temperature of the electric motor 11 a fromthe detected rotational speed and the motor current of the electricmotor 11 a. Moreover, the air conditioner controller 20 calculates thedetected temperature of the electric motor 11 a is in which range of thecontrol characteristic for the cooling operation mode, and the processgoes to step S400.

If it is determined at step S110 that the cooling/heating selectingswitch of the air conditioner operating panel 40 is switched to theheating operation mode, the air conditioner controller 20 calculates atstep S220 a control amount of the opening degree of the first electricexpansion valve 12 so that the discharge refrigerant pressure Pd of theelectric compressor 11 can become the target high pressure Po, which isdetermined based on the exterior-side refrigerant temperature Tho of theexterior-side heat exchanger 13.

Next, at step S310, the air conditioner controller 20 selects thecontrol characteristic for the cooling operation mode. Then, based onthe selected control characteristic, the air conditioner controller 20calculates and detects the temperature of the electric motor 11 a fromthe detected rotational speed and the motor current of the electricmotor 11 a. Moreover, the air conditioner controller 20 calculates thedetected temperature of the electric motor 11 a is in which range of thecontrol characteristic for the heating operation mode, and the processgoes to step S400. The processes at steps S310, S320 correspond to acontrol characteristic selector.

As explained above, in each operation mode, a control characteristicadapted for the operation mode is selected from two or more controlcharacteristics in which the criterion values are different, and thetemperature of the electric motor 11 a is detected based on the selectedcontrol characteristic. By determining whether the detected temperatureof the electric motor 11 a is larger than (or equal to) the criterionvalue of the selected control characteristic or not, it is possible toperform the determination in the temperature protection control for theelectric motor 11 a. Thereby, the reliability of the temperatureprotection control of the electric motor 11 a is raised.

Third Embodiment

Next, a third embodiment of the present invention will be describedhereafter. Elements that are substantially the same as or equivalent tothose in the first and second embodiments have the same referencenumerals as in the first and second embodiments, and are not describedagain.

In the above-described second embodiment, a certain controlcharacteristic is selected in accordance with the operation mode, andthe temperature of the electric motor 11 a is calculated and detectedfrom the detection value of the inverter unit 19, on the basis of theselected control characteristic. In contrast, in the third embodiment,two or more control characteristics in which the criterion values aredifferent are memorized beforehand in ROM etc. of the air conditionercontroller 20. Then, a certain control characteristic is selected fromthe two or more control characteristics in accordance with a degree ofsuperheat of the refrigerant at the suction side of the electriccompressor 11, and the temperature of the electric motor 11 a iscalculated from the detection value of the inverter unit 19.

Specifically, suction refrigerant pressure Ps of the electric compressor11 is detected by the suction pressure sensor 35, and suctionrefrigerant temperature sensor Ts of the electric compressor 11 isdetected by the suction refrigerant temperature sensor 36. Then,saturated vapor temperature of the refrigerant is calculated from thedetected suction refrigerant pressure Ps, and the degree of superheat SHof the refrigerant at the suction side of the electric compressor 11 iscalculated from the suction refrigerant temperature Ts and the saturatedvapor temperature. Alternatively, the suction refrigerant pressure Psmay be evaluated from blown-out air temperature Te of the evaporator 5,which is detected by a post-evaporator air temperature sensor 33.

If the degree of superheat SH of the refrigerant at the suction side ofthe electric compressor 11 is large, the temperature of the electricmotor 11 a rises. Therefore, a control characteristic in which thecriterion value is set low is selected from two or more controlcharacteristics. If the degree of superheat SH of the refrigerant at thesuction side of the electric compressor 11 is small, the temperature ofthe electric motor 11 a does not rise so much. Therefore, a controlcharacteristic in which the criterion value is set high is selected fromtwo or more control characteristics.

As explained above, based on the degree of superheat SH of therefrigerant at the suction side of the electric compressor 11, a certaincontrol characteristic is selected from predetermined two or morecontrol characteristics in which the criterion values are different andthe temperature of the electric motor 11 a is calculated and detectedbased on the certain control characteristic. Thus, it is possible toperform the determination in the temperature protection control for theelectric motor 11 a. Thereby, the reliability of the temperatureprotection control of the electric motor 11 a is raised.

Here, the control process in the third embodiment is applicable not onlyto the heat pump refrigerant cycle system described in the secondembodiment, but also to the refrigerant cycle system described in thefirst embodiment.

Other Embodiments

The present invention is not limited to the above-described embodiments,and may be modified variously as follows.

(1) In the above-described embodiments, the temperature of the electricmotor 11 a of the electric compressor 11 is calculated and detected,using the control characteristic that associates the temperature of theelectric motor 11 a with the rotational speed and the motor current ofthe electric motor 11 a. The present invention is not limited to thisconfiguration. For example, the temperature of the electric motor 11 amay be detected by a temperature sensor for detecting intra-motortemperature of the electric motor 11 a, a temperature sensor fordetecting temperature of a housing of the electric motor 11 a, etc.

(2) In the above-described embodiments, the opening degrees of theelectric expansion valves 12, 16 are directly adjusted in thetemperature protection control for the electric motor 11 a of theelectric compressor 11. The present invention is not limited to thisconfiguration. For example, the discharge refrigerant pressure Pd of theelectric compressor 11 may be lowered by lowering the target highpressure that is determined based on the temperature (exterior-siderefrigerant temperature) Tho of the refrigerant at the outlet side ofthe exterior-side heat exchanger 13 or the use-side heat exchanger 6,which acts as the heat-radiating heat exchanger.

(3) In the above-described embodiments, the temperature protectioncontrol for the electric motor 11 a of the electric compressor 11 isperformed by controlling the opening degree of the electric expansionvalve 16 not to decrease when the temperature protection for theelectric motor 11 a of the electric compressor 11 is necessary.Alternatively, it is also possible to raise the rotational speed of theelectric motor 13 b of the cooling fan (first electric blower) 13 a inaddition to the control of the opening degree of the electric expansionvalve 16.

By raising the rotational speed of the cooling fan 13 a, the temperatureof the refrigerant at the outlet side of the heat-radiating heatexchanger 6, 13 is lowered, and the target high pressure is lowered.Thereby, the pressure (discharge refrigerant pressure Pd) of therefrigerant at the outlet side of the electric compressor 11 is lowered,and the temperature rise of the electric motor 11 a is avoided.

(4) Moreover, it is also possible to lower the rotational speed of theelectric motor 4 a of the electric blower (second electric blower) 4when the temperature protection for the electric motor 11 a of theelectric compressor 11 is necessary.

By lowering the rotational speed of the electric blower 4, the coolingcapacity of the evaporator 5 is raised, and the degree of superheat ofthe refrigerant at the suction side of the electric compressor 11 islowered. Thereby, the pressure (suction refrigerant pressure Ps) of therefrigerant at the suction side of the electric compressor 11 islowered, and the temperature rise of the electric motor 11 a is avoided.

(5) Further, the interior/exterior air switching door 3 c may beswitched to the interior air mode when the temperature protection forthe electric motor 11 a of the electric compressor 11 is necessary. Byswitching the interior/exterior air switching door 3 c to the interiorair mode, the cooling capacity of the evaporator 5 is lowered, and thedegree of superheat of the refrigerant at the suction side of theelectric compressor 11 is lowered. Thereby, the pressure (suctionrefrigerant pressure Ps) of the refrigerant at the suction side of theelectric compressor 11 is lowered, and the temperature rise of theelectric motor 11 a is avoided.

(6) In the above-described second embodiment, different controlcharacteristics, in which the criterion values are different, areselected for the cooling operation mode and the heating operation mode.The present invention is not limited to this configuration. For example,the control characteristic for the heating operation mode may be appliedin dehumidifying operation mode. A control characteristic for thedehumidifying operation mode may be selected in the dehumidifyingoperation mode.

(7) Moreover, in the above-described second embodiment, even in thecooling operation mode, the degree of superheat of the refrigerant atthe suction side of the electric compressor 11 is small when theelectric compressor 11 has just started. Therefore, the same controlcharacteristic as that for the heating operation mode may be selectedwhen the degree of superheat of the refrigerant is smaller than apredetermined value, and the same control characteristic as that for thecooling operation mode may be selected when the degree of superheat ofthe refrigerant is larger than a predetermined value.

(8) Moreover, the above-described refrigerant cycle system 10 may beapplied to an ejector cycle system that is publicly known by thedocuments such as JP3322263B1, which corresponds to U.S. Pat. Nos.6,477,857 and 6,574,987. In this case, the variable throttle mechanismis replaced by an ejector provided with a variable needle.

(9) In the above-described embodiments, the refrigerant cycle system 10according to the present invention is applied to a vehicular airconditioning system. The present invention is not limited to theseexamples. For example, the refrigerant cycle system according to thepresent invention may be applied to a fixed air conditioning system forhome use or business use. Moreover, the refrigerant cycle system may beapplied not only to an air conditioning system that can be switchedbetween the cooling operation mode and the heating operation mode butalso to a dedicated cooling system.

(10) Moreover, in the above-described refrigerant cycle system 10, thekind of the refrigerant is not specified. The refrigerant may bechlorofluorocarbons, chlorofluorocarbon substitutes such as HCrefrigerants, carbon dioxide (CO₂) that can be applied to both asupercritical vapor compression refrigerant cycle system and asubcritical vapor compression refrigerant cycle system, etc.

Additional advantages and modifications will readily occur to thoseskilled in the art. The invention in its broader terms is therefore notlimited to the specific details, representative apparatus, andillustrative examples shown and described.

1. A refrigerant cycle system comprising: an electric compressor thatincludes a compression mechanism, which sucks and compressesrefrigerant, and an electric motor, which drives the compressionmechanism and is cooled by the refrigerant at a suction side of thecompression mechanism; a variable throttle mechanism that decompressesthe refrigerant discharged from the electric compressor; a motortemperature detector that detects a temperature of the electric motor; amotor protection determiner that determines whether the temperature ofthe electric motor detected by the motor temperature detector is equalto or higher than a criterion value; and a motor protection controllerthat controls the variable throttle mechanism so that opening degree ofthe variable throttle mechanism does not decrease when the motorprotection determiner determines that the temperature of the electricmotor is equal to or higher than the criterion value.
 2. The refrigerantcycle system according to claim 1, further comprising a drive circuitthat controls operation of the electric motor, wherein: the drivecircuit detects a motor current, which is an electric current outputtedto the electric motor, and a rotational speed of the electric motor; andthe motor temperature detector detects the temperature of the electricmotor by calculating the temperature of the electric motor from therotational speed and the motor current of the electric motor, which aredetected by the drive circuit, with reference to a controlcharacteristic data map, which is prepared in advance and indicates arelationship of the temperature of the electric motor with respect tothe rotational speed and the motor current of the electric motor.
 3. Therefrigerant cycle system according to claim 2, wherein: the criterionvalue is specified in the control characteristic data map to correspondsto the rotational speed and the motor current of the electric motor; andthe motor protection determiner determines whether the temperature ofthe electric motor calculated by the motor temperature detector is equalto or higher than the criterion value specified in the controlcharacteristic data map.
 4. The refrigerant cycle system according toclaim 3, wherein: the criterion value specified in the controlcharacteristic data map is a first criterion value; a second criterionvalue that is higher than the first criterion value is specified in thecontrol characteristic data map; the motor protection determinerdetermines whether the temperature of the electric motor calculated bythe motor temperature detector is equal to or higher than the firstcriterion value; the motor protection determiner further determineswhether the temperature of the electric motor calculated by the motortemperature detector is equal to or higher than the second criterionvalue when the motor protection determiner determines that thetemperature of the electric motor calculated by the motor temperaturedetector is equal to or higher than the first criterion value; the motorprotection controller controls the variable throttle mechanism so thatthe opening degree of the variable throttle mechanism does not decreasewhen the motor protection determiner determines that the temperature ofthe electric motor calculated by the motor temperature detector is equalto or higher than the first criterion value and is lower than the secondcriterion value; and the motor protection controller controls thevariable throttle mechanism so that the opening degree of the variablethrottle mechanism increases when the motor protection determinerdetermines that the temperature of the electric motor calculated by themotor temperature detector is equal to or higher than the secondcriterion value.
 5. The refrigerant cycle system according to claim 3,further comprising: a suction refrigerant superheating degree detectorthat detects a degree of superheat of the refrigerant at the suctionside of the electric compressor; and a control characteristic selectorthat selects one control characteristic data map from among a pluralityof control characteristic data maps, each of which is prepared inadvance and indicates a relationship of the temperature of the electricmotor with respect to the rotational speed and the motor current of theelectric motor, on a basis of the degree of superheat of the refrigerantdetected by the suction refrigerant superheating degree detector,wherein the motor protection determiner determines whether thetemperature of the electric motor calculated by the motor temperaturedetector is equal to or higher than the criterion value specified in theone control characteristic data map.
 6. The refrigerant cycle systemaccording to claim 3, wherein the refrigerant cycle system is a heatpump system that operates in a cooling operation mode in which therefrigerant cools heat-exchange target fluid and in a heating operationmode in which the refrigerant heats the heat-exchange target fluid, therefrigerant cycle system further comprising a control characteristicselector that selects a first control characteristic data map in thecooling operation mode from among a plurality of control characteristicdata maps, each of which is prepared in advance and indicates arelationship of the temperature of the electric motor with respect tothe rotational speed and the motor current of the electric motor, andselects a second control characteristic data map in the heatingoperation mode from among the plurality of control characteristic datamaps so that the criterion value specified in the first controlcharacteristic data map is lower than the criterion value specified inthe second control characteristic data map, wherein the motor protectiondeterminer determines whether the temperature of the electric motorcalculated by the motor temperature detector is equal to or higher thanthe criterion value specified in the first control characteristic datamap or the second control characteristic data map that is selected bythe control characteristic selector.
 7. The refrigerant cycle systemaccording to claim 1, further comprising a heat-radiating heat exchangerthat cools the refrigerant at a discharge side of the electriccompressor, wherein: the variable throttle mechanism decompresses therefrigerant at an outlet side of the heat-radiating heat exchanger sothat a pressure of the refrigerant at the discharge side of the electriccompressor becomes closer to a target high pressure that is determinedon a basis of a temperature of the refrigerant at the outlet side of theheat-radiating heat exchanger; and the motor protection controllerlowers the target high pressure when the temperature of the electricmotor detected by the motor temperature detector is equal to or higherthan the criterion value.
 8. The refrigerant cycle system according toclaim 7, further comprising: a first electric blower that blows exteriorair to the heat-radiating heat exchanger; and a first electric blowercontroller that controls a rotational speed of the first electricblower, wherein the first electric blower controller raises therotational speed of the first electric blower when the motor protectiondeterminer determines that the temperature of the electric motordetected by the motor temperature detector is equal to or higher thanthe criterion value.
 9. The refrigerant cycle system according to claim6, further comprising: an evaporator that vaporizes the refrigerantdecompressed by the variable throttle mechanism; a second electricblower that blows heat-exchange target fluid to the evaporator; and asecond electric blower controller that controls a rotational speed ofthe second electric blower, wherein the second electric blowercontroller lowers the rotational speed of the second electric blowerwhen the motor protection determiner determines that the temperature ofthe electric motor detected by the motor temperature detector is equalto or higher than the criterion value.
 10. The refrigerant cycle systemaccording to claim 6, further comprising: an evaporator that vaporizesthe refrigerant that is decompressed by the variable throttle mechanism;and an interior/exterior air switcher that switches an air introducingmechanism between an interior air mode, in which air blown to theevaporator is introduced from an interior, and an exterior air mode, inwhich the air blown to the evaporator is introduced from an exterior,wherein the interior/exterior air switcher switches the air introducingmechanism to the interior air mode when the motor protection determinerdetermines that the temperature of the electric motor detected by themotor temperature detector is equal to or higher than the criterionvalue.
 11. The refrigerant cycle system according to claim 1, whereinthe motor temperature detector includes a motor temperature detectionsensor for detecting the temperature of the electric motor.